The present invention generally relates to a method and an apparatus for detecting leakage in a flow control valve and more particularly, relates to a method and an apparatus for detachably mounting a leakage detection device to a bellow-type flow control valve for detecting leakage of a facility gas into a high purity process gas that is controlled by the flow control valve.
In the semiconductor process industry, a large variety of different ultra pure gases are used in the fabrication plants. These gases include bulk gases such as N2, O2, H2 and Ar which are normally used in very large quantities, and specialty gases such as He, ASH3, PH3, SiH4, NH3 and NF3 which are used only in small quantities. In general, the bulk gases are used for purging of chambers, oxidation and cleaning of wafers, while the specialty gases are used as reactant or etching gases.
The bulk gases are normally stored in large storage facilities, for instance, N2 can be supplied from a liquified-nitrogen storage tank located in the gas yard or delivered from a pipeline from a remote air-separation plant; O2 and Ar can be supplied from liquified gas storage tanks; while H2 can be delivered from either a liquified-gas storage tank or a bank of high-pressure gas cylinders. The bulk gases are normally passed through purifiers and gas filters for removing impurities and contaminating particles before allowed to enter a gas-distribution piping system installed inside a cleanroom. On the other hand, the speciality gases are normally stored in small quantities in gas cylinders and are sent directly to the process tools from cylinders stored inside gas cabinets in the cleanroom. The gas cabinets are exhausted safety enclosures that contain the gas cylinders and the necessary gas handling equipment. The gas cabinets serves a major function of allowing purging and safe exchange of the speciality gas cylinders. The gas handling equipment, which includes gas panels incorporating all components for the control and monitoring of high purity gases. In most semiconductor fabrication facilities, the gas cabinet contains at least two process cylinders to allow easy switch-over when one cylinder is empty. In addition, another cylinder of inert gas such as nitrogen is provided for purging the piping line.
In most fabrication processes, the supply pressure for the bulk and the speciality gases is kept at under 10 Kg/cm2. A few exceptions exist such as chlorine and dichlorosilane. At each point of use, the pressure of the bulk or speciality gas has to be independently and locally controlled by a series of flow control valves, pressure regulators, pressure sensors and particle filters located inside a gas manifold box. The precise pressure required for each bulk or speciality gases to be delivered to a specific process tool is determined by the process requirement. In most semiconductor cleanroom facility, one or more gas manifold boxes are installed nearby to each process tool to facilitate gas distribution and control.
A frequently used tool for gas distribution or control is a bellow-type flow control valve for controlling the flow of high purity process gases. One of such commercially available valves is a Nupro valve. Due to the large number of different process gases used in a single process machine, i.e. in a chemical vapor deposition chamber, a large number of bellow-type flow control valves are required for controlling fluid conduits in which process gases pass through.
An illustration of a typical bellow-type flow control valve 10 and its application in controlling a high purity process gas are shown in FIG. 1. To operate the bellow-type flow control valve 10, a facility gas such as a facility nitrogen is normally required. The facility gas is normally controlled by a shut-off valve 14 for controlling its flow. A suitable shut-off valve may be one that is an electromagnetic valve shown in FIG. 1 of a normal-closed type. When a high pressure facility gas, such as nitrogen, is applied to the normal-closed valve 14, the valve 14 opens to let the facility gas to flow therethrough into a fluid conduit 16. The facility gas then enters the bellow-type flow control valve 10 to compress a bellow to open a flow passageway therein allowing a high purity process gas to pass through conduit 12 for feeding to a process chamber (not shown). When the high purity process gas is no longer needed, the bellow-type flow control valve 10 is closed by closing the shut-off valve 14 and thus stopping the flow of the facility gas.
The bellow-type flow control valves have been widely used in gas flow control in the industry, and particularly, in the semiconductor fabrication industry. Problems occur when bellow-type flow control valves have been used for a length of time which frequently leads to a malfunction of the bellow inside the valve control mechanism. When the problem is serious, proper performance of the flow control valve can be affected to render the valve ineffective. One of the frequently observed problems is the leakage of facility gas into a high purity process gas flow due to a leakage existed in the bellow inside the flow control valve. Since a facility gas such as nitrogen frequently contains various impurities of oxygen, hydrogen, water vapor or other impurities, a severe contamination of the high purity process gas occurs which leads to serious fabrication problems. Since a large number of bellow-type flow control valves are normally utilized on a single process machine, it is an insurmountable task to identify a specific flow control valve that is responsible for a leakage. Conventionally, the only way to find a defective valve is by a trial and error method, i.e. by replacing one valve at a time until the contamination problem is solved. This turns out to be an extremely time and labor consuming task resulting in a significant loss in fabrication yield.
It is therefore an object of the present invention to provide a method for detecting leakage in a flow control valve that does not have the drawbacks or shortcomings of the conventional methods.
It is another object of the present invention to provide a method for detecting leakage in a bellow-type flow control valve by connecting a leakage detection apparatus in-between a shut-off valve and the flow control valve.
It is a further object of the present invention to provide a method for detecting leakage in a bellow-type flow control valve by a leakage detection apparatus which includes a mass flow controller and a recording means for connecting between a shut-off valve and the flow control valve.
It is still another object of the present invention to provide a method for detecting leakage in a bellow-type flow control valve by temporarily connecting a leakage detection apparatus in-between a facility gas source and the flow control valve.
It is another further object of the present invention to provide a method for detecting leakage in a bellow-type flow control valve wherein a leakage detection apparatus is connected in-between a shut-off valve and the flow control valve by quick disconnect means.
It is yet another object of the present invention to provide a leakage detection apparatus which includes a mass flow controller and a recording means for detecting leakage through a bellow-type flow control valve.
It is still another further object of the present invention to provide a flow control apparatus that is equipped with a built-in leakage detection device including a shut-off valve, a fluid conduit, a leakage detection device and a bellow-type flow control valve.
It is yet another further object of the present invention to provide a flow control apparatus that is equipped with a built-in leakage detection device which is connected to the flow control apparatus by quick disconnect valves.
In accordance with the present invention, a method and an apparatus for detecting leakage in a flow control valve are provided.
In a preferred embodiment, a method for detecting leakage in a flow control valve can be carried out by the steps of connecting a shut-off valve between a facility gas source and a first end of a fluid conduit, connecting a second end of the fluid conduit to a facility gas inlet on the flow control valve, providing a leakage detection apparatus in the fluid conduit in fluid communication with the first end and the second end of the conduit, the leakage detection apparatus consists of a mass flow controller for detecting a fluid flow through the conduit and a recording means for recording the fluid flow through the conduit, flowing a facility gas flow into the flow control valve for opening the flow control valve to allow a process gas to pass therethrough, shutting-off the facility gas flow by the shut-off valve to stop the process gas from passing therethrough, and detecting any residual facility gas flow through the flow control valve into the process gas by the leakage detection apparatus.
The method for detecting leakage in a flow control valve may further include the step of opening the flow control valve by compressing on a bellow situated in the valve by the facility gas. The method may further include the step of connecting the leakage detection apparatus into the fluid conduit by a quick disconnect device. The method may further include the step of providing the flow control valve in a Nupro valve. The method may further include the step of providing the facility gas source in a general nitrogen gas source. The method may further include the step of providing the flow control valve in a bellow-type flow control valve for controlling the flow of a high purity process gas. The method may further include the step of providing the shut-off valve in a normal-closed valve. The method may further include the step of recording a gas pressure of the facility gas flown through the mass flow controller by the recording means, the step of recording a gas flow rate of the facility gas flown through the mass flow controller by the recording means, and the step of recording a gas pressure of the facility gas flown through the mass flow controller for a time period of about 1 second.
The present invention is further directed to a flow control apparatus that is equipped with a built-in leakage detection device including a shut-off valve mounted in-between and in fluid communication with a source of facility gas and a first end of a fluid conduit, a fluid conduit for connecting in fluid communication with the shut-off valve at a first end and with a facility gas inlet of a flow control valve at a second end, a flow control valve operated by the facility gas for allowing or disallowing a process gas flow to pass therethrough, and a built-in leakage detection device mounted in the fluid conduit in fluid communication with the first end and the second end of the conduit, the built-in leakage detection device includes a mass flow controller and a recording means for detecting leakage of the facility gas into the process gas flow.
In the flow control apparatus that is equipped with a built-in leakage detection device, the built-in leakage detection device is detachably mounted in the fluid conduit. The flow control valve is used to regulate flow of a process gas that has 99% or higher purity. The flow control valve is a bellow-type valve operated by the shut-off valve. The flow control valve may be a Nupro valve. The leakage of the facility gas into the process gas flow occurs through a defective bellow in the flow control valve. The facility gas may be a general nitrogen gas. The shut-off valve may be a normal-closed on/off valve. The recording means records a pressure of the facility gas that passes through the mass flow controller.